How to use (old) Computer Modern for `math.cal`? And why context matters?

Questions
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1

My friend wants to use the Computer Modern Math font for math.cal.
We manage to define our own cal as the following, but we encounter issues on the positioning of sub/superscripts. And it’s quite strange that the result changes if we prepend a context.

// Using cmsy10.ttf:
#let cal(s) = text(font: "cmsy10", math.upright(s))

// Using context + cmsy10.ttf:
#let cal(s) = context text(font: "cmsy10", math.upright(s))

图片
图片747×252 28 KB

$cal(P)_n$ $cal("P")_n$
Standard :white_check_mark: Good :sweat_smile: Bad kerning, but good height
cmsy10.ttf :x: Bad kerning and height :sweat_smile: Bad kerning, but good height
context + cmsy10.ttf :sweat_smile: Bad kerning, but good height :sweat_smile: Bad kerning, but good height
Full code 
#let cal(s) = text(font: "cmsy10", math.upright(s))
#let ccal(s) = context cal(s)

#set text(fallback: false)
#set raw(lang: "typc")
#table(
  columns: 3,
  stroke: none,
  align: (end, center, center),

  table.header([], `$cal(P)_n$`, `$cal("P")_n$`),
  table.hline(),
  table.vline(x: 1),

  [Standard], $std.math.cal(P)_n$, $std.math.cal("P")_n$,
  [`cmsy10.ttf`], $cal(P)_n$, $cal("P")_n$,
  [`context` + `cmsy10.ttf`], $ccal(P)_n$, $ccal("P")_n$,
)

Could anyone offer any advice or explanation? Thanks in advance.

Futher info about the font

We mean the the old Computer Modern Math, the default font in LaTeX (without loading new packages like newcomputermodern and unicode-math).

The original Computer Modern Math predates OpenType, and only exists as antique font formats in typical TeX distributions. The matplotlib project has converted the font to OTF.
That is the font file used above, and can be downloaded from lib/matplotlib/mpl-data/fonts/ttf/cmsy10.ttf.

Note that cmsy10.ttf maps cal(P) to P (ASCII P), rather than 𝒫 (Unicode math symbol, U+1D4AB). Therefore, we added upright to our customized cal.

Relates to Is there still difference between `$upright(…)$` and `$"…"$` in v0.14.0?

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2

Another friend 请输入密码 remapped the character map and added MathKernInfo & MathItalicsCorrectionInfo. The fixed font resolves all problems.

#show math.equation: set text(font: (
  // Fixed font
  (name: "Computer Modern Symbol", covers: regex("[𝒜ℬ𝒞𝒟ℰℱ𝒢ℋℐ𝒥𝒦ℒℳ𝒩-𝒬ℛ𝒮-𝒵]")),
  "New Computer Modern Math",
))

图片
图片790×291 42.3 KB

Full code 
#set page(height: auto, width: 240pt, margin: 1em)

#set align(end)

Typst default $cal(K M Z), cal(P)_n, cal(T)^p$

#[
  #let cal(s) = text(font: "cmsy10", math.upright(s))
  Original font  $cal(K M Z), cal(P)_n, cal(T)^p$
]

#[
  #let cal(s) = context text(font: "cmsy10", math.upright(s))
  Original font with context $cal(K M Z), cal(P)_n, cal(T)^p$
]

#[
  #show math.equation: set text(font: (
    (name: "Computer Modern Symbol", covers: regex("[𝒜ℬ𝒞𝒟ℰℱ𝒢ℋℐ𝒥𝒦ℒℳ𝒩-𝒬ℛ𝒮-𝒵]")),
    "New Computer Modern Math",
  ))
  Fixed font $cal(K M Z), cal(P)_n, cal(T)^p$
]

Download CMSY10-fix_cmap_kerning.otf

Recorded in 怎么把 cal 字体变成 LaTeX 里 mathcal 默认的那种？ | Typst 中文社区导航.

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